Enhanced kinetics in Cu-doped LiFePO4 cathodes due to local structural disorder

The widespread adoption of LiFePO4 as a cathode material is hindered by its intrinsically low ionic and electronic conductivity. While transition metal doping is a recognized strategy to mitigate these limitations, the precise mechanistic underpinnings remain elusive. Here, we present a comprehensive multi-scale investigation into copper-doped LiFePO4 (LiCuxFe1−xPO4) that not only demonstrates a dramatic enhancement in performance but also uncovers the fundamental role of local structural disorder. Our study, which integrates advanced synchrotron-based characterizations including X-ray pair distribution function (PDF) analysis, and X-ray absorption spectroscopy (XAS) with Raman spectroscopy, electrochemical analysis, and molecular dynamics simulations, reveals a compelling structure-property relationship. We show that despite a negligible change in the average crystal structure, Cu doping induces significant local structural disorder. This effect is directly responsible for a remarkable enhancement in lithium-ion diffusion by nearly two orders of magnitude and a staggering six-fold increase in specific capacity for the optimal doping concentration (x=0.05) compared to the undoped material. Our molecular dynamics simulations further provides qualitative understanding on how the local disorder significantly lowers the energy barriers for Li-ion migration. This work offers microscopic insights, establishing the local structural disorder as a critical enabler of superior cathode kinetics and providing a new paradigm for designing high-performance electrochemical materials. Transitional metal doping of LiFePO4 cathodes improves ionic and electrical conductivity, but the mechanism behind this is unclear. Here, copper doping is found to enhance local structural disorder, lowering the energy barrier for Li-ion diffusion.